Metal-forming devices using direct electrode contact



June 8, 1965 H- P. FURTH 3,137,532

METAL-FORMING DEVICES USING DIRECT ELECTRODE CONTACT Filed Dec. 26, 1861 I INVENTOR JZmow IZ/efi/ BY 4 .E%

,4 Trap/v5 Y by a pulsed magnetic field,

United States Patent s,1s7,ss2 i METAL-FDRMING DEVIQES USENG DIRECT ELEGTRODE CfiNTACT Y Harold P. Furtli, Berkeley, alit., assignor to Advanced Kinetics, Inc., Costa Mesa, Calih, a corporation or California Filed Dec. 26, 1961, Ser. No. 161,923

' 9 Claims. (Cl. 72-5d) f The present invention relates generally to metal-forming forming devices where current is passed directly to the metal surface of the work by means of electrodes, rather than being induced thereon.

A piece of metal can be formed by pressing on it with a pulsed magnetic field. For this purpose a current must fiow on the surface of the metal, atright; angles to the magnetic field, and the resultant motor force forms the metal against a mold.

In magnetic metal forming evices of the known art the pulsed magnetic field induces 21 current on the metal surface by transformer action.

Energy losses such asstray inductive energy storage inherent in transformer operation result therefrom. Additionally high ohmic losses are generated by the two complete current circuits required for the forming process: i.e. the primary circuit through the conductor generating the magnetic field and the secondary circuit through the metal work piece. Accordingly it is an object of this invention to provide a magnetic metal forming device of improved elficiency.

The device of the present invention provides a magnetic metal-forming device in which the surface of the metal work piece is part of the circuit that generates the pulsed magneticfield, contact to the surface being made by specially designed contact electrodes, suitable for passing large current densities. A single complete current circuit is provided for generating the magnetic fieldand producing the current in the work piece which interacts with the magnetic field to provide magnetic pressure on the work piece. Stray magnetic fields and ohmic losses are maintained at a minimum greatly reducing the energy requirements for the forming operation.

It is therefore another object of this inventionto provide a magnetic metal forming device having low energy losses. 7

and more particularly to.

in the process of magnetic metal-forming a magnetic field of strength B is transiently created outside the surface of the work to be formed. There results a magnetic pressure on the surface. A current orthogonal to the magnetic field, and of density must how on the metal surface, per unit length along the magnetic field. 7

If the magnetic forming device is aclosed coil, held near the work, and then pulsed to provide a transient magnetic field, then a current corresponding to that in Equation 2 is transiently induced on the surface of the work. The magnetic forming devices described inthe present invention do not constitute closed coils or circuits in themselves, but have electrodes to make contact with the surface of the work and complete the circuit in this way. Then the current described by Equation 2 is passed directly ontothe surface of the work by means of the electrodes, instead of being induced.

A technical problem that must be solved in the directcontact method is'how to pass very high current densities onto the surface of the work without damaging the contact electrodes and without doing excessive damage to the surface of the work at the contact points. For magnetic forming, fields of approximately 100,000 gauss strength are needed in order to produce sufiicient pressure;

For 190,000 gaussstrength, Equation l-gives a pressure of 5600p.s.i., and Equation 2 requires a current density of 80,006 amperes per unit length along. the magnetic field. If the contact from the'torming device were made by means of ordinary blunt electrodes,-severe sparking and erosion would result at such high current densities.

The present invention makes use of spring contacts, which are so disposed that the current flowing through the contacts presses them against the surface of the work with approximately the same large pressure that is being usedfor the forming operation itself. This high pressure contact permits the needed high current densities It is a further objecticf this invention to provide a magnetic metal forming device in Will'lh'lh magnetic field andthe current in the metal work piece are provided;

forming sheet metal against According to a principal aspect of the invention a conductor is responsively connected to a high energy current source and shaped to provide a magnetic field of predetermined strength. An electrically conductive metal work piece is positioned within said magnetic field at a predetermined distance from the conductor; Means are provided for conductively connecting said conductor to the metal work piece for providing a primary circuit through the conductor and the metal workpiece. The

current flowing in the "conductor generates the magnetic field and the current flowing in the metal work piece to be passed without excessive damage. The contacts are made of very hard low-sparking materials such as beryllium copper. Y I

Referring now to the drawing, in the forming device shown in FIGURE 1, a capacitor bank 11 having a high energy charge thereon is discharged by means of a switch 12 through the transmission lines 13 and the contact electrodes 14, and along the surface of the work, in this case a piece of sheet metal =15. A single complete current circuit is created flowing along the path illustrated by the arrows 33. A magnetic field appears within this circuit and interacts with the current flowingfalong the surface of the metal piece 15 to push the sheet metal against a mold .16 by means of magnetic pressure exerted on the work piece 15.; The current flowing in the sheet metallS is concentrated mostly in the region covered by the portions 13am the transmission line th-at are parallel to and located at a predetermined distance from the sheetmetal 15, and this is the region where the greatest pressure is exerted, The portions 16a of the transmission line in FIG. 1 are shown as rectangular plates, =butmore generallythey can have any outline, such as a ziz-Zag or a semicircle, or they may have constrictions where the cur rent is concentrated and the local magnetic field and pressure' are correspondingly increased. The contact -electrodes '14 are so disposed that the current flowing from the transmission line '13 to the metal piece 15 acts to improve the contact with the metal piece 15. Each of the electrodes 14 is U shaped With one end being part of the shaped portion 13a to form an inner leg of the U shape and the other end bent to form an outer leg of the U shape The outer leg of the electrodes is parallel to and touches the metal piece 15 to provide conductive contact between the portionslSa and the metal piece 15. Current flowing in the portions 13a and the outer leg of the electrodes 14 generates a magnetic pressure which acts to push the outer leg of the electrodes 14 against the metal piece 15 to further improve the contact between the portions 13a and the metal piece 15.

The forming device shown in FIGURES 2a and 2b is an example of a generalization shown in FIGURE -l. In FIG. 2a the transmission line 17 now has a portion 17a lying parallel to the sheet metal 18, which has a serpentine form. The current is passed to the sheet metal through the contacts 19, and returns on the surface of the sheet metal in a serpentine pattern closely matching that of the transmission line 17a. As a result, a corrugated pat-tern is formed on the sheet metal 18. The sheet metal 18 may either be driven into a suitably corrugated mold 16, or else a second corrugator (not shown) may be applied on the back side of the sheet metal 18, with the lines of maximurn'pressure for one icorr ugator matching the lines of minimum pressure for the other corrugator. The magnetic field pattern set up in the corrugation process is indicated 'by the arrows 20 in FIG. 2b. The currents flowing in the transmission line system are indicated by the arrows 21.

Referring now to FIG. 3 there is illustrated a magnetic forming device for expanding tubes. In the forming device shown in FIG. 3, a current is'passed from a capacitor bank 22 through a coaxial transmission line consisting of an inner cylinder 23 and an outer tube 25, which make contact through the electrodes 24 to the tube 26 that is to be expanded. The pathof the current is indicated by the arrows 27, and the resultant azimuthal magnetic field iis indicated by the arrows 28. A single current path is provided forgenerating the magnetic field and the interacting current to provide the magnetic pressure to expand the tube '26.

'A particular, advantage of the device of the present invention lie-s in its electrical efficiency. Unlike the induction method olf -theknown art providing strong inductive energy losses and high ohmic losses with the two current circuits the device of this invention reduces losses to a minimum by providing a single current path. Magnetic pressures of higher strength and greater efliciency than heretofore possible are generated. 7

Various of the novel features of the present invention are set forth in the following claims.

I claim:

1. In a device for forming metal by magnetic pressure;

a high energy current source,

a conductor responsively connected to said current source and shaped to provide a magnetic field of predetermined strength, 7 h

an electrically conductive metal work piece positioned within saidmagnetic held at a predetermined distance (from said conductor, h a

and means for conductively connecting said conducto to said metal work piece for providing a primary circuit through said conductor and said metal work piece, the .current fiowing in said conductor generating said magnetic field and the current flowing in said metal work piece interacting with said mag- -netic;field to provide magnetic pressure on said metal work piece for shaping the work piece.

2, Themetal forming device of claim 1 wherein said means for conductively connecting said conduct-orto' said metal work piece comprises a pair of spring contact electrodes for connecting the ends of said conductor to the ends of said metal work piece.

3. A magnetic metal forming device comprising,

a transmission line responsively connected to a current or" the forming device source and having a portion shaped to provide a magnetic field of high strength, an electrically conductive metal work piece positioned within said magnetic field at a predetermined distance from said transmission line,

the shaped portion of said transmission line being parallel to said metal work piece, the ends of said shaped portion being bent to form U shaped portions each having an outer leg parallel to and touching said metal work piece to provide conductive con-tact between said metal work piece and said transmission line, whereby a single current path is created through said transmission line and said metal workpiece for generating said magnetic field and providing magnetic pressure on said metal work piece for shaping the workpiece. 4. The metal fiorming device recited in claim 3 wherein predetermined parts of the shaped portion of said transmission line are constricted for concentration of current and magnetic field strength.

5. In .a magnetic metal forming device having a transmission line and a metal work piece adjacent to and parallel to said transmission line, means for providing a' single current path through said transmission line and said metal work piece comprising,

means for condufctively connecting said transmission line to said work piece,

and means for applying a high. energy current pulse to said transmission line, whereby the current flowing in said transmission line generates a magnetic field of predetermined strength and the current flowing in said metal work piece interacts with the magnetic held to provide magnetic pressure on said metal work piece for shaping the work piece.

6. Themagnetic metal forming device recited in claim 5 wherein said means for conductively connecting said transmission line to said work piece comprises a pair of U shaped contact electrodes connecting the ends of said transmission line to the ends otf'said met-a1 work piece, the outer leg of each said U shaped portion parallel to and touching said metal work piece to provide conductive contact between said metal work piece and said transmission line whereby current flowing in said outer leg interacts with said magnetic field'to provide pressure on said outer leg maintaining said outer leg in contact with said metal work piece.

7. A magnetic metal forming device comprising,

a high energy current source,

a first transmission line responsively connected to said current source'and shaped in a serpentine form to provide a magnetic field of predetermined strength,

an electrically conductive metal work piece positioned within said magnetic =field and adjacent to said transmission line,

means for conductively connecting said transmission line -to said metal work piece for providing a current path through said transmission line and said metal Work piece, the current flowing in said first transmission line generating said magnetic field and the current flowing in said metal work piece interacting with said magnetic field to provide magnetic pressure on said metal work piece,

mold means adjacent said metal work piece,

said metal work piece positioned between said mold means and said transmission line whereby said magnetic pressure causes said metal work piece to conform to the surface of said mold means.

8.- A magnetic metal forming device comprising,

a high energy current source,

an electrically conductive inner tube responsively conv nected to said current source to provide amagnetic field of predetermined strength,

an electrically conductive outer tube Work piece formed in spatial relation about said inner tube and positioned within said magnetic field,

and means for conductively connecting said inner tube iconduetively connecting said conductor to said metal to said outer tube work piece for providing a current path through said inner tube and said outer tube, the current flowing in said inner tube generating said magnetic field and the current flowing in said outer tube interacting with said magnetic field to provide magnetic pressure on said outer tube, whereby said outer tube is expanded corresponding to the strength of said magnetic field.

work piece by direct contact of said conductor to said metal work piece for providing a current path through said conductor and said metal work piece, the current flowing in said conductor interacting with said magnetic field to provide magnetic pressure on said metal work piece to form said metal work piece.

References Cited by the Examiner UNITED STATES PATENTS 9. In .a process for (forming an electrically conductive 10 metal Work piece the steps comrrising, 2,976,907 3/61 Harvey et al. 113-44 placing said metal work piece adjacent a conductor, WILLIAM J STEPHENSON Primary Examiner applying a high energy current pulse to said conductor to generate a magnetic field of high strength, CHARLES W. LANHAM, Examiner. 

1. IN A DEVICE FOR FORMING METAL BY MAGNETIC PRESSURE; A HIGH ENERGY CURRENT SOURCE, A CONDUCTOR RESPONSIVELY CONNECTED TO SAID CURRENT SOURCE AND SHAPED TO PROVIDE A MAGNETIC FIELD OF PREDETERMINED STRENGTH, AN ELECTRICALLY CONDUCTIVE METAL WORK PIECE POSITIONED WITHIN SAID MAGNETIC FIELD AT A PREDETERMINED DISTANCE FROM SAID CONDUCTOR, AND MEANS FOR CONDUCTIVELY CONNECTING SAID CONDUCTOR TO SAID METAL WORK PIECE FOR PROVIDING A PRIMARY CIRCUIT THROUGH SAID CONDUCTOR AND SAID METAL WORK PIECE, THE CURRENT FLOWING IN SAID CONDUCTOR GENERATING SAID MAGNETIC FIELD AND THE CURRENT FLOWING IN SAID METAL WORK PIECE INTERACTING WITH SAID MAGNETIC FIELD TO PROVIDE MAGNETIC PRESURE ON SAID METAL WORK PIECE FOR SHAPING THE WORK PIECE. 